1. Field of the Invention
The invention relates to a device and an improved and simplified method for determining and correcting the angular offset of two shafts of machines or machine components which due to their parallel offset are connected to one another by way of two universal joints and a third shaft which connects the two universal joints.
2. Description of Related Art
It is conventional to equalize offsets between two shafts which connect engines and driven assemblies to one another via two universal joints and a third shaft. But this arrangement can only equalize parallel offsets. When the two shafts are not aligned exactly parallel to one another, serious damage often occurs due to an angular offset.
The two types of offsets, specifically parallel offset and angular offset, can be easily and accurately determined with optoelectronic alignment devices. However, this is only possible in the simpler case when the two shafts which are connected to one another coaxially. These optical alignment devices based on lasers or other light sources and photosensitive detectors (PSD, CCD arrays or CMOS arrays) are described in German Patent DE 39 11 307 (which corresponds to U.S. Pat. No. 5,026,998) and German Patent DE 33 20 163 (which corresponds to U.S. Pat. No. 4,698,491). In these documents, alignment devices are described which, on the one hand, contain a light source in a measurement head and a detector in a second measurement head. In the measurement head, both the incidence position and also the incidence direction of a light beam can be measured by there being two detectors which can be read out two-dimensionally in succession in the beam path of the measurement head. This arrangement can be achieved, for example, via a beam splitter. On the other hand, measurement devices are also described in which one measurement head contains both a light source and also a two-dimensional detector, while the second measurement head contains a reflector, for example, in the form of a ridge prism. The alignment devices which are described in the aforementioned documents use light beams of point cross section and detectors which can be read out two-dimensionally.
German Patent Application DE 10 2006 023 926 and corresponding U.S. Pat. No. 7,672,001 describe alignment devices in which light beams are fanned out in more than one direction transversely to the propagation direction. Some embodiments call for each measurement head to contain both a light source and also a detector. The aforementioned optical alignment devices assume that the points of impact of the light beam or light beams on the detector or detectors is measured in several (at least three, but usually four or even five or more) rotary positions of the two shafts.
German Patent DE 33 35 336 and corresponding U.S. Pat. No. 4,518,855 describe an alignment device in which each measurement head contains both a light source and also detectors which can be read out two-dimensionally according to the site of incidence and angle of incidence. This measurement device is able to determine a misalignment according to angular and parallel offset in only one rotary position of the two shafts from one measurement of the points of impact on the detectors when the orientation of this rotary position and the points of impact are known for well aligned shafts by a comparison measurement on a single straight shaft. Measurements in different angular positions on the shafts which are to be aligned are, however, also fundamentally possible.
Often, special matching devices are employed for the use of these optoelectronic alignment devices for shafts which do not run coaxially, which therefore have a parallel offset and are connected via two universal joints and a third shaft. This device is shown in European Patent EP 1 430 995 and corresponding U.S. Pat. No. 7,242,465. The disadvantage in the use of these devices is that, as described in these documents, often the third shaft must be removed. Moreover, complicated handling of the devices and execution of a host of steps are necessary which make the performance of the determination of an angular offset complex and susceptible to errors. Thus, it can happen that a machine, once it has been correctly aligned, is unintentionally shifted when the third shaft is re-installed. Another problem is that these devices are produced with overly large tolerances so that the measurement of the angular offset becomes too inexact due to play. The prior art in this document involves a pivot joint which has to be positioned along a blade. This blade is mounted to one of the two shafts, and the pivot joint with the sensor head on it is arranged in a position where the axis of the pivot joint matches the axis of the other shaft to be aligned. The position of the axis of this pivot joint must be adapted to the radial distance between the two shafts which are to be brought into alignment.
U.S. Pat. No. 4,708,485 describes a rotatable holder for the measurement head of an alignment instrument. This rotatable holder is mounted to the housing of a machine component whose shaft is to be brought into alignment with the shaft of another machine component. The axis of this rotatable holder is positioned coaxially with the machine housing. As this housing of the machine component is not necessarily positioned coaxially with the shaft in this housing, the shaft position has to be monitored with additional sensors.